1. Field of the Invention
The present invention relates to a data communication system, a data communication method, a data communication apparatus, and a digital interface. In particular, the present invention pertains to a network for transmitting communication data (including image data) and command data together at a high speed, and a communication protocol that can be applied for the network.
2. Related Background Art
Conventionally, hard disks and printers are the peripheral devices that are most frequently employed with personal computers (PCs). One of these peripheral devices is connected to a PC via a special input/output interface or via a general-purpose digital interface, such as a SCSI (a small computer system interface).
Recently, however, AV (Audio/Visual) devices, such as digital cameras and digital video cameras, have become popular, and taken together they constitute another type of peripheral that can be used with a PC. Such an AV (Audio/Visual) device can be connected to a PC via an interface.
FIG. 1 is a diagram illustrating a conventional communication system that comprises a PC and an AV device.
In FIG. 1, 101 denotes an AV device (a digital camera), 102 denotes PC and 103 denotes a printer.
The digital camera 101 comprises: a memory 104, in which image data is compressed and recorded; a decoder 105, for expanding the compressed image data stored in the memory 104 in order to decode them; an image processing unit 106; a D/A converter 107; a display unit 108 that includes an EVF; and a special digital I/O unit 109, for connecting the digital camera 101 and the PC 102.
The PC 102 comprises: a special digital I/O unit 110, for connecting the PC 102 to the digital camera 101; an operation unit 111, including a keyboard and a mouse; a decoder 112, for expanding the compressed image data in order to decode them; a display unit 113; a hard disk 114; a memory 115, such as a RAM; an MPU 116; a PCI bus 117; and a SCSI interface, for connecting the PC 102 to the printer 103.
The printer 103 comprises: a SCSI interface 119, for connecting the printer 103 to the PC 102; a memory 120; a printer head 121; a printer controller, for controlling the operation of the printer 103; and a driver 123.
In a conventional communication system the special digital interface (digital I/O unit) 109 of the digital camera 101 and the digital interface (SCSI interface) 119 of the printer 103 are not compatible, and one can not be directly connected to the other. Therefore, when, for example, the digital camera 101 is to transmit a still image to the printer 103, the PC must serve as a relay.
The conventional special digital interface 109 and the conventional SCSI interface 119 have many shortcomings: their data transfer rates are low, especially when, for a still image or a moving picture, there is a large amount of data to be transferred from an AV device; thick cables are employed for parallel communication; only a small number and a few types of peripheral devices can be connected; the connection system is limited; and data transfers can not be performed in real time.
A fast, high-performance, next generation digital interface that can resolve the above shortcomings is one that conforms to the well known IEEE (the Institute of Electrical and Electronics Engineers, Inc.) 1394-1995 interface standards.
A digital interface that conforms to the IEEE 1394-1995 interface standards (hereinafter referred to as a 1394 interface) has the following features.
(1) The data transfer speed is high.
(2) The real-time data transmission system, i.e., the isochronous transmission system, and the asynchronous transmission system are supported.
(3) A connection configuration (topology) having a high degree of freedom can be obtained.
(4) The Plug and Play function and the active line detachment function are supported.
However, while in the IEEE 1394-1995 standards the physical and electrical connections for a connector and the most fundamental data transmission systems are defined, a data type, a data format and a communication protocol to be employed for the exchange of data are not defined.
Since according to the IEEE 1394-1995 standards a response for the receipt of a packet is not defined for the isochronous transmission system, there is no way by which to ensure that an individual isochronous packet has been received. Therefore, the isochronous transmission system can not be employed when a plurality of sets of sequential data are to be transmitted, or when data in a file is to be transmitted by dividing the data into a plurality of data sets.
In the isochronous transmission system according to the IEEE 1394-1995 standards, the total number of communications is limited to 64, even though there is an empty space in a transmission band. Therefore, the isochronous transmission system is not adequate for multiple communications carried by a small transmission band.
According to the IEEE 1394-1995 standards, the transmission of data must be halted when a bus is reset because the power to a node is turned on or off, or when the connection or disconnection of the node is established. However, according to the IEEE 1394-1995 standards, when data transmission is halted (stopped) due to the resetting of a bus or to an error that occurs during transmission, the contents of the data that are lost can not be identified. Further, very complicated communication processing must be performed to resume the transmission.
The bus resetting function is a function for automatically identifying a new topology and for setting an address (node ID) that is allocated to the node. According to this function, the Plug and Play function and the active line detachment function can be provided by applying the IEEE 1394-1995 standards.
For a communication system that conforms to the IEEE 1394-1995 standards, real time processing is not required, and no specific communication protocol has been proposed that can be used for dividing a comparatively large amount of object data that must be reliable (e.g., still image data, graphics data, text data, file data or program data) into more than one data segment, and for sequentially transmitting the data segments.
In addition, for a communication system that conforms to the IEEE 1394-1995 standards, no specific communication protocol has been proposed that can be used to implement data communications among a plurality of devices by employing a communication method for the asynchronous broadcasting of data.
It is one object of the present invention to solve the above described problems.
It is another object of the present invention to provide a technique, for a data communication system, a data communication method, a data communication apparatus and a digital interface, whereby it is ensured that object data for which real time processing is not required can be sequentially transmitted.
It is an additional object of the present invention to provide a technique, for a data communication system, a data communication method, a data communication apparatus and a digital interface, whereby sequential transmission of data between a source node and one or more destination nodes can be satisfactorily halted through only simple processing, without complicated communication procedures being required.
As one preferred embodiment for such objects, according to the present invention, a communication system comprises:
a source node adapted to transmit data packets;
a destination node adapted to receive the data packets transmitted from the source node; and
a controller adapted to manage a logical connection between the source node and the destination node,
wherein the destination node is adapted to abort communication between the source node and the destination node if the destination node receives an abort packet transmitted from the controller, and wherein the destination node is adapted to disconnect the logical connection after the communication is aborted by the abort packet.
As one more preferred embodiment of the present invention, a communication method for a communication system comprising a source node adapted to transmit data packets, a destination node adapted to receive the data packets transmitted from the source node, and a controller adapted to manage a logical connection between the source node and the destination node, comprises the steps of:
aborting communication between the source node and the destination node if the destination node receives an abort packet transmitted from the controller; and
disconnecting the logical connection after the communication is aborted by the abort packet.
As another preferred embodiment of the present invention, a data communication method for a destination node adapted to receive data packets transmitted from a source node comprises the steps of:
aborting communication between the source node and the destination node if the destination node receives an abort packet transmitted from a controller which manages a logical connection between the source node and the destination node; and
disconnecting the logical connection after the communication is aborted by the abort packet.
As an additional preferred embodiment of the present invention, a destination node adapted to receive data packets transmitted from a source node, comprises:
aborting means adapted to abort communication between the source node and the destination node if the destination node receives an abort packet transmitted from a controller which manages a logical connection between the source node and the destination node; and
disconnecting means adapted to disconnect the logical connection after the communication is aborted by the abort packet.
Still other objects of the present invention and the advantages thereof will become fully apparent during the course of the following detailed description given for the embodiments.